Next step is getting the extruder tuned. I grabbed a piece of filament from the scrap box, and went "What is this, actually?" Some googling found several methods of testing, most of which weren't practical: Burning a bit and sniffing it - no open fire in FabLab. Dunk in acetone - don't have any. Test in the extruder - not good when the extruder isn't tested yet. Break it quickly - it whitens a bit and breaks, but I wouldn't call it "snapping". Rubbing it against clothing and smelling it - no noticable smell (hints at PLA). Heating with a properly controlled soldering iron - seems to not melt a lot @200. Dipping in warm water does make it bend easily, that strongly indicates PLA.
From the last test I'm going with it being PLA. And indeed, some properly marked rolls of PLA behave the same way.
With the glass plate one, Z level is 1.6 and it's perfectly flat. Turns out I'd missed the bit about clipping on the glass plate. I have the clips, and they just barely fit in the opening, if I place them just right. Adjusting the firmware to have a Z home of 201,7. Then re-measured and subtracted another 0,2 mm to allow for expansion, and set the Z screw pointers.
Annoying thing about the clips is that one is right where the extruder comes down if I just home and then down.
Strange hiccup while heating up the extruder, the temp reading stayed the same for a while then jumped. That's potentially dangerous, but it did end up at the right temperature.
Alas, actual extrusion failed. A small amount of the previous black filament drippled out, but I was unable to force the new orange on in by hand, and the extruder motor refused to turn in either direction more than a brief second at the start.
Took out the hobbed bolt to see if it was ok, looks fine to me. Loosened the idler on the side, fastened it, no difference.
Took out the idler and looked inside. Aha! A stump of old filament from mid-bolt down. Heating up the hot-end, I was able to pull this out. Didn't help on getting more in.
On a lark, I looked at what happeend when the idler was in but the hobbed bolt was out. Turns out my filament wasn't even making it through to the hobbed bolt. When in doubt, more violence! Pressing harder moved the idler aside. Knowing now how much to press I was able to do this with the hobbed bolt in, and have it grab. I then hand-cranked until I started feeling resistance, then turned on the heater and handcranked out black goo till it turned white.
Still no luck running the extruder motor, though. Tried measuring the inputs, but that's not so easy with a stepper motor's varying input. Looked like the right-hand input was at least different than the others when measuring alternating current across them, so maybe there's something up with that one.
Enough for tonight, alas. Tomorrow a more physical battle awaits (if anybody but me are crazy enough to go fight in this heat:)